It is known to provide an image processing system in which a user can instruct the performance of an image processing operation on image data by selecting a corresponding operation icon on a display, and can combine these operations into a sequence (Hirakawa et al, Iwata, S; Tahara; Tahara, Y; Tanaka, M; Ichikawa, T "A framework for construction of Icon Systems", Proc. 1988 IEEE Workshop on Visual Languages pages 70 to 77). In this known system, two sequence assembly methods are provided; a "bottom up" method, in which a user proceeds to assemble a sequence in a linear fashion, each operation being executed before the next can be added to the sequence, and a "top down" method in which dummy data entries can be used to construct a sequence of operations for subsequent execution. Problems with the first of these methods are that because interpretation and execution take place during the sequence construction, the execution (and hence user response) is slow, and that the sequence must have been pre-written in advance, in full detail, by the user (which removes much of the interactiveness or the system). The second method purports to overcome these problems, but is in fact also not interactive since a sequence is specified in isolation from its execution, without a user viewing the effects of the sequence.
A similar "visually programmable" image analysis system is shown in V. Haarslev and R. Moller, "Visualisation of Experimental Systems" Proc. 1988 IEEE Workshop on Visual Languages pages 175 to 182.